A continuation of the study of the structural and mechanical basis of aortic valvular function will be carried out. Precise measurements of the dynamic and static pressures beneath the aortic valve, within the Sinuses of Valsalva, and immediately above the aortic valve, will be made and analyzed to determine the hemodynamic forces responsible for aortic valve opening and closing. Ultrastructural analysis of left ventricular myocardium will be continued in order to correlate the ultrastructural changes with the clinical course of patients undergoing heart surgery. Cloth covered aortic valvular prostheses treated with an antibacterial agent will be analyzed in vivo to determine their ability to prevent bacterial endocarditis.